(1) Field of the Invention
This invention relates to thermal management structures and, more particularly, to heat sinks and related thermal dissipation devices molded of conductive loaded resin-based materials comprising micron conductive powders, micron conductive fibers, or a combination thereof, homogenized within a base resin when molded. This manufacturing process yields a conductive part or material usable within the EMF or electronic spectrum(s).
(2) Description of the Prior Art
Modern electronic systems create many thermal management problems. For example, integrated circuits operating at very high switching speeds generate a large amount of heat due to IR losses. This heat must be efficiently removed from the integrated circuit device to maintain high-speed performance and to prevent a device failure. In addition, high current switches generate a large amount of heat loss due to IR that must be dissipated from the device to avoid a failure. Power oriented circuits, such as DC-DC converters, power supply circuits, etc., also generate significant heat that must be dissipated to protect the power devices.
A typical approach to removing heat from an integrated circuit, switching transistor, or power-oriented circuit is the use of a heat sink. A heat sink is a structure that is attached to a heat-producing device such that thermal energy is conducted out from the heat producer and into the heat sink. Further, the heat sink dissipates this thermal energy at a rate sufficient to maintain thermal energy flow from the heat-producing device into the heat sink. As a result, the heat sink maintains the temperature of the device at a level that will prevent reduced performance or catastrophic failure. Typical heat sinks are formed from metal. For example, aluminum is frequently used as a heat sink material due to the excellent thermal conductivity and relatively low weight of this metal. The typical heat sink is attached, for example, to a metal tap on the IC or transistor device to achieve a good thermal path between device and heat sink. Further, the heat sink structure typically is constructed to have a large surface area by, for example, using a large number of parallel fins such that the heat sink presents a large surface for removing heat by convection.
Another type of thermal management device is a heat pipe. A heat pipe is a pipe containing a small amount of liquid. Heat from a heat source, such as an electronic device, causes the liquid to vaporize. As this liquid vaporizes, the liquid absorbs the latent heat of vaporization from the heat source. The vapor travels away from the heat source, through the pipe, to the cool end of the pipe. At the cool end of the pipe, the vapor condenses to liquid to complete the heat transfer. Typical heat pipes are constructed of metal and may further contain a lining of wicking material. Heat pipes are often coupled with heat sinks to form a heat transfer system where the heat pipe conducts heat away from the heat source and where a heat sink structure is used to enhance thermal transfer at the condensing end of the heat pipe.
The present practice of forming heat sink or heat pipe structures from metal has several disadvantages. Among these disadvantages are the material and manufacturing cost of metal, especially copper, and the weight of the metal. Reduction of system cost and weight by changing the composition of the heat sink and/or heat pipe is therefore a key objective of the present invention.
Several prior art inventions relate to conductive resin compositions and structures. U.S. Pat. No. 6,565,772 to Schneck teaches a conductive resin comprising resin, a cure accelerant, and a conductive particulate. The conductive resin is applied to hide welding imperfections in automobile manufacturing. U.S. Pat. No. 6,451,418 to Tobita describes a substrate or a chip package constructed from a heat conductive resin material. The heat conductive resin material comprises polybenzasol fibers oriented in the thick direction of the substrate. U.S. Pat. No. 6,284,817 to Cross et al discloses a conductive resin-based material including aluminum oxide and zinc oxide particles. The material is used in one embodiment to bond a packaged transistor to an aluminum heat sink. U.S. Pat. No. 6,597,063 to Shimizu et al shows a package for a semiconductor power device. A high heat conductive resin is formed between the power device and the heat sink in one embodiment. U.S. Patent Application 2003/0183379 to Krassowski et al teaches a composite heat sink comprising a graphite base and conductive plastic fins. The conductive plastic comprises graphite flakes in a resin base.